Hydraulic lock for a linear actuator

ABSTRACT

The piston of a pneumatic actuator is releasably locked in extended position by a hydraulic device responsive to the air pressure in the actuator cylinder. A hydraulic supply reservoir feeds hydraulic fluid through a check valve to a chamber containing a displacement piston attached to the actuator piston so that the pistons are permitted to move to extended position but prevented from returning. A controllable release valve bypassing the check valve is provided to allow return of the hydraulic fluid from the chamber to the reservoir to permit retraction of the actuator piston.

United States Patent [72] Inventor Thomas W. Shearer, Jr.

Auburn Heights, Mich. [2|] Appl. No. 881,236 [22] Filed Dec. 1, 1969 (45] Patented Sept. 7, I971 [73] Assignee General Motors Corporation Detroit, Mich.

[541 HYDRAULIC LOCK FOR A LINEAR ACTUATOR 2 Claims, 3 Drawing Figs.

[52] US. 91/45 [51] Int. Cl 523d 1/08 [50] Field ofSearch 91/4l,45

[56] References Cited UNITED STATES PATENTS 2,339,024 1/1944 Markson 91/45 2,891,514 6/l959 Moeller Primary ExaminerMartin P. Schwadron Assistant Examiner-Clemens Schimikowski Att0rneys.lean L. Carpenter, Paul Fitzpatrick and Warren D. Hill 72 I? a /:i r 2 ii if a 11 m v v PATENTEDSEP "nan 3503205 If W {f w a COMPRESSED I AIR SOURCE I EFF- 115; 1 (v if) w w :"E': mlluflifi 62 7 fj i iii INVENI'UR.

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ATTORNEY HYDRAULIC LOCK FOR A LINEAR AGTUA'TOR This invention relates to a hydraulic lock for a linear actuator.

In the use of linear fluid actuators, it is often desirable to hold or lock the actuator in extended position. This is particularly desirable where it is required that the actuator resist large opposing forces and the motive fluid is highly compressible in nature, e.g., compressed air or fluid supplied at a low pressure. In the past, complicated mechanical locks have been proposed, but these generally are subject to wear, not only of the lock itself but of the actuator.

It is therefore a general object of this invention to provide a hydraulic lock for a linear actuator.

It is a further object of this invention to provide a hydraulic lock for a pneumatic actuator.

It is an additional object to provide a hydraulic lock which is easily adapted to existing fluid pressure actuators.

It is yet another object of this invention to provide a hydraulic lock for a fluid pressure actuator which is responsive to the motive fluid pressure of the actuator so that the lock is operable when actuating fluid pressure is applied to the actuator and is released when the actuating pressure is relieved.

It is still another object of the invention to provide a hydraulic lock having a predetermined limit of locking force and will yield without damage to the actuator or the lock.

' The invention is carried out by providing an adapter for a linear motor including an auxiliary piston engaging the actuated member i of the motor for movement therewith, a chamber containing a portion of the auxiliary piston and a supply for feeding hydraulic fluid to the chamber during movement of the actuated member and the auxiliary piston in one direction and for preventing fluid flow from the chamber to prevent movement of the piston and the actuating member in the other direction. A release mechanism is provided in the adapter for selectively allowing escape of hydraulic fluid from the chamber to permit movement of the actuated member in the other direction.

The invention is further carried out by providing a hydraulic lock for a linear fluid pressure actuated motor including a displacement piston connected with the piston rod of the motor for movement therewith, a chamber for receiving the displacement piston, a reservoir of hydraulic fluid subjected to the motive fluid pressure of the motor, a check valve permitting fluid flow only from the reservoir to the chamber to maintain the chamber full of hydraulic fluid during extension of the piston rod and the displacement piston, and a pilot-operated poppet valve responsive to the motive fluid pressure in the actuator to permit flow from the chamber to the reservoir when the motive fluid pressure is relieved.

The above and other advantages will be made more apparent from the following specification taken in conjunction with the accompanying drawings wherein like reference numerals refer to like parts and wherein:

FIG. 1 is a cross-sectional view of a pneumatic actuator provided with a hydraulic lock according to the invention;

FIG. 2 is a cross-sectional view of the hydraulic lock taken along lines 2-2 of FIG. 1; and,

FIG. 3 is a diagrammatic illustration of a suggested application of the hydraulic lock according to the invention.

The invention is applicable to linear motors of any type regardless of the type of motive power used, however, for purposes of illustration, the preferred embodiment of the device is described as applied to a pneumatic actuator.

Referring to FIGS. 1 and 2 of the drawings, an actuator includes a pneumatic cylinder 12 having a piston 14 reciprocably mounted therein and an actuated member or piston rod member 16 secured to the piston 14 for movement therewith. A port 18 connected to a conduit 20 is provided at the right end of the cylinder for admitting air pressure thereto for moving the piston 14 and the piston rod 16 toward the left to an extended position, and a port 22 connected to a conduit 24 is provided at the left end of the cylinder 12 to admit air pressure thereto'for returning the piston and piston rod to the retracted or idle .position as shown. In place of the usual cylinder head or closure, hydraulic lock adapter 26 is attached to the cylinder 12 as by fasteners 27. The adapter 26 contains a bore 28 closed by a plug 29 to define a chamber 30 axially aligned with the piston rod I6. A further bore 32 at one end of the chamber 30 and coaxial therewith slidably receives a displacement piston 34 which is attached at one end to the piston I4 on the axis thereof, the other end extending into the chamber 30. O-rings 35 provide a seal between the bore 32 and the piston 34. Another bore 36 in the adapter 26 is arranged parallel with the bore 28 and is in communication with v the cylinder 12. A spoollike piston 38 in the, bore 36 is retained by a snapring 40 and defines at the right end of the bore variable volume reservoir 42 for hydraulic fluid. Air pressure in the cylinder 12 forces the piston 38 against the hydraulic fluid to apply pressure thereto and the piston 38 shifts to accommodate changes in volume of the hydraulic fluid in the reservoir. The reservoir 42 is connected to the chamber 30 by two passages 44 and 46 in parallel. The reservoir 42, the chamber 30 and the passages are filled with hydraulic fluid to form a closed hydraulic circuit. A bore 48 intersecting the passage 46 is closed by a plug 50 and contains a check valve 52 and a compression spring 54 abutting against the plug 50 and the check valve 52 to urge the check valve into the passage 46. The check valve 52 is so disposed that fluid flow from the reservoir 42 to the chamber 30 is permitted but flow in the opposite direction is prevented. The passage 44 is intersected by a small-diameter bore 56 which is coaxial with a cylinder 58 with a diameter larger than that of the bore 56 and forms an extension thereof. A poppet valve 60 is reciprocably mounted in the bore 56 for selectively blocking the passage 44. A pilot piston 62 in the cylinder 58 is rigidly connected with the poppet valve 60. O-rings 64 and 68 are located in appropriate annular grooves in the poppet valve and piston respectively to provide seals. A closure member 68 comprises a cylindrical body 70 fitting within the cylinder 58 and a flange 72 surrounding the opening of the cylinder 58 to accommodate fasteners 74 holding the closure member 68 in place. An O-ring 76 is seated in an annular groove in the cylindrical body 70 to provide a seal. A threaded aperture 78 through the closure member is connected to a conduit 80.

It is preferred that the conduit 80 be connected with the conduit 20 so that when fluid pressure is applied thereto the pistons 14 and 62 will be advanced or retracted simultaneously. For some applications, however, it may be desired to independently connect the conduits 20 and 80 to the fluid pressure source to achieve independent actuation of the pistons.

In operation, air pressure is supplied to the cylinder I2 through the conduit 20 to urge the piston 14 and the displacement piston 34 to the left. The air pressure within the cylinder acts on the spoollike piston 38 to pressurize the hydraulic fluid within the reservoir 42 so that the hydraulic fluid will flow from the reservoir and through the passage 46 and the check valve 52 into the chamber 30 thereby maintaining the chamber full of hydraulic fluid. Assuming the conduits 20 and 80 to be interconnected, the air pressure will act on the piston 62 to seat the poppet valve 60 closing the passage 44. However, when the actuated member 16 is in any extended position, and an opposing force is applied thereto which tends to return the piston rod toward retracted position, an equal force will be developed in the hydraulic fluid trapped within the chamber 30 thereby preventing a retractive movement of the displacement piston 34 and the piston rod 16. So long as the hydraulic force tending to unseat the poppet valve 60 does not exceed the pneumatic force exerted on the top of the piston 62, the poppet valve 60 will, of course, remain seated. Since the piston area is much greater than the effective valve area e.g., 20 times larger, a relatively small fluid pressure applied to the piston 62 will enable the poppet valve 60 to maintain a much larger hydraulic pressure within the chamber 30. At the same time, however, there is a limit to the amount of force on the piston rod I6 that can be resisted by the poppet valve 60 so that when such great force is encountered, the valve 60 will open to automatically provide a safety release of fluid from the chamber to the reservoir 42. To retract the piston rod in,

air pressure is applied to the cylinder 12 through port 22 and air pressure is relieved at port l8. Assuming the conduit 80 is connected with the conduit 20, pressure will also be relieved in the cylinder 58 to permit opening of the poppet valve 60 in response to the hydraulic pressure in the chamber 30. The actuator piston 14 and the displacement piston 34 will be forced to the right and the hydraulic fluid will flow from the chamber 30 through the passage 44 to the reservoir 42 displacing the spoollike piston 38 to the left.

FIG. 3 illustrates a specific application of the hydraulic lock to a resistance welding apparatus. A frame 84 supports the actuator and its adapter 26. The piston rod 16 carries a mover ble electrode 86, and a stationary electrode 88 aligned with the movable electrode 86 is supported by the frame 84. Workpieces 90 to be welded are interposed between the electrodes. The electrodes 86 and 88 are energized by a welding power supply 92. The conduits 80 and 20 of the hydraulic lock are interconnected and they, as well as the conduit 24, are connected to a control valve 94 in turn is connected to a compressed air source 96. By manipulating the control valve 94, pressure is applied to the conduits 20 and 80 to extend the piston rod 16 thereby clamping the workpieces 90 between the electrodes 86 and 88. The power supply 92 is then caused to supply welding current to the electrodes. During the welding period, the workpieces 90 thermally expand and therefore attempt to move apart the electrodes 86 and 88. The electrode 86, however, is held immovable with respect to the hydraulic lock adapter 26 so that an electrode force much greater than the original clamping force is developed. Normally the hydraulic lock will be designed to withstand the force applied by the expanding workpieces 90. in the event of an unusually large force the lock will release as described above to limit the force to some predetermined maximum which depends upon the pressure applied to the pilot piston 62 and the ratio of the area of the pilot piston to the poppet valve area. This release feature prevents damage to the welding apparatus including the actuator 10 and the hydraulic lock adapter 26.

It will be recognized by those versed in the art that the hydraulic lock adapter can be fitted to many types of existing actuators with only minor modifications of the actuators.

The embodiment of the invention described herein is for purposes of illustration. The scope of the invention is intended to be limited only by the following claims:

it is claimed:

1. in a fluid pressure actuator having an actuated member movable to an extended position upon application of fluid pressure thereto, a hydraulic lock for retaining the member in extended position comprising chamber acting through the piston against the actuated member to thereby effect locking of the actuated member 1 in its extended position.

the supplying means comprising a reservoir containing hydraulic fluid, means for subjecting the hydraulic fluid within the reservoir to the fluid pressure in the actuator and for isolating the hydraulic fluid from the actuator fluid, a passage interconnecting the reservoir and the chamber, and a check valve in the passage arranged to permit flow of hydraulic fluid only to the chamber.

2. In a fluid pressure actuator having an actuated member movable to an extended osition upon application of fluid pressure thereto, a hydrau to lock for retaining the member in extended position comprising a housing secured to the actua tor, the housing containing:

an elongated chamber filled with hydraulic fluid coaxial with the actuated member,

a displacement piston attached to the actuated member for movement therewith and extending partially into the chamber,

a variable-volume reservoir containing hydraulic fluid,

means for transmitting pressure from the actuator fluid to thc'hydraulic fluid in the reservoir and for isolating the hydraulic fluid from the actuator fluid,

a first flow path from the reservoir to the chamber, a poppet valve in the first flow path operated by a pilot piston responsive to fluid pressure for closing the first flow path when fluid pressure is applied to the pilot piston,

a second flow path in parallel with the first, a check valve in the second flow path for allowing flow only from the reservoir to the chamber whereby when fluid pressure is applied to the pilot piston movement of the actuated member to its extended position is accompanied by the flow of hydraulic fluid to the chamber and movement of the actuated member in the opposite direction is prevented, and when fluid pressure at the pilot piston is relieved fluid flow is permitted from the chamber to the reservoir to allow the actuated member to move from its extended position.

32 3 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Segtember 7, 1971 Patent No. 0 205 Dated Inventor(s) Thomas W. Shearer, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In Column 3, line 22, after "94" insert which In Column 4, line 8, change "piston" to position --I Signed and sealed this 16th day of May 1972.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOTTSCHALK Commissioner of Patents Attesting Officer 

1. In a fluid pressure actuator having an actuated member movable to an extended position upon application of fluid pressure thereto, a hydraulic lock for retaining the member in extended position comprising a chamber filled with hydraulic fluid secured to the actuator, a piston in the chamber operatively connected to the actuated member for movement therewith, means for supplying hydraulic fluid to the chamber during movement of the actuated member and the piston to the extended piston and for preventing fluid flow from the chamber so that a force tending to return the actuated member from its extended position is opposed by an equal force developed in the hydraulic fluid in the chamber acting through the piston against the actuated member to thereby effect locking of the actuated member in its extended position. the supplying means comprising a reservoir containing hydraulic fluid, means for subjecting the hydraulic fluid within the reservoir to the fluid pressure in the actuator and for isolating the hydraulic fluid from the actuator fluid, a passage interconnecting the reservoir and the chamber, and a check valve in the passage arranged to permit flow of hydraulic fluid only to the chamber.
 2. In a fluid pressure actuator having an actuated member movable to an extended position upon application of fluid pressure thereto, a hydraulic lock for retaining the member in extended position comprising a housing secured to the actuator, the housing containing: an elongated chamber filled with hydraulic fluid coaxial with the actuated member, a displacement piston attached to the actuated member for movement therewith and extending partially into the chamber, a variable-volume reservoir containing hydraulic fluid, means for transmitting pressure from the actuator fluid to the hydraulic fluid in the reservoir and for isolating the hydraulic fluid from the actuator fluid, a first flow path from the reservoir to the chamber, a poppet valve in the first flow path operated by a pilot piston responsive to fluid pressure for closing the first flow path when fluid pressure is applied to the pilot piston, a second flow path in parallel with the first, a check valve in the second flow path for allowing flow only from the reservoir to the chamber whereby when fluid pressure is applied to the pilot piston movement of the actuated member to its extended position is accompanied by the flow of hydraulic fluid to the chamber and movement of the actuated member in the opposite direction is prevented, and when fluid pressure at the pilot piston is relieved fluid flow is permitted from the chamber to the reservoir to allow the actuated member to move from its extended position. 